Nauru detention centre insiders say there were clear warning signs of a riot

Immigration and law enforcement insiders have told the ABC it was obvious trouble was brewing at the Nauru detention centre well before last week's destructive riot.

The site's former manager Greg Lake says the Immigration Department failed to learn from the disastrous Christmas Island inferno two years ago.

An Australian Federal Police (AFP) officer has also told 7.30 he warned the Government that trouble was looming and that an AFP presence is the only way to ensure safety at detention centres.

Key points

Nauru detention centre riot cost taxpayers $60 million

The site's former manager says there were clear signs trouble was brewing

An AFP officer also says he warned the Government of looming unrest

Their accounts of rising tension are supported by Salvation Army staff working on Nauru

It has also been revealed the centre's security staff ordered riot gear

But the equipment did not arrive in time for Friday's incident

On Friday night the centre exploded into violence unprecedented on Nauru, with the accommodation destroyed and rocks thrown at guards.

The ABC understands 125 asylum seekers have been charged over the riot, which left taxpayers with a bill of at least $60 million.

Mr Lake says there were clear signs trouble was coming to the centre, which reopened in September last year.

"The asylum seekers who were there when I was on Nauru where involved in all sorts of expressions of their frustration," he told 7.30.

"Everything from huge levels of depression and self-harm, through to voluntary starvation, demonstrations and protest action.

"Occasionally that would break out in physical expressions of frustration in violence and things like that, even down to lip sewing and all sorts of horrific behaviour which is sourced from a place of vulnerability and immense frustration."

I'm not surprised in the slightest and I know some of my colleagues were also concerned about this sort of eventuality.

Greg Lake, former site manager of Nauru detention centre

Mr Lake, who quit the Immigration Department in April, says it failed to learn from the March 2011 riots on Christmas Island.

"I'm aware of colleagues of mine who... were concerned the same thing was about to happen in the regional processing centres either on Manus or Nauru," he said.

"Turns out it was Nauru. I'm not surprised in the slightest and I know some of my colleagues were also concerned about this sort of eventuality."

AFP officer warned of looming unrest

AFP officer Brendan Thomson is currently on unpaid sick leave.

He is involved in a protracted dispute with the organisation that started when he wrote to the AFP Commissioner urging him not to withdraw a team of riot officers just four months before the Christmas Island riot.

In August last year Sergeant Thomson's lawyers wrote to then-home affairs minister Jason Clare warning the same thing could happen on Nauru.

The letter said the Government needs to "address systemic threats to health and safety... ensure appropriate critical incident measures are in place for Nauru and Manus Island".

It warned that otherwise, "destructive behavioural patterns will emerge... with significant injury to life and property".

Sergeant Thomson received a brief reply directing him to the Commonwealth Ombudsmen.

Sergeant Thomson says it is time there was a permanent AFP presence in detention centres.

"I just don't understand at this stage and the amount of damage and cost to the Australian taxpayer that we aren't seeing uniformed police maintaining and establishing or re-establishing the rule of law and law and order in the detention centres, where it clearly is not able to be maintained by the service providers," he said.

Salvation Army staff say riot was 'inevitable'

The account of rising tension on the island is supported by Salvation Army staff working on the island.

Twenty-five of them have broken ranks with their organisation to speak out.

Mark Issacs, a former Salvation Army employee providing humanitarian support on the island, says there were warnings a riot was coming.

As shocked as we are, we feel it was an incident that was inevitable considering the conditions that the men are kept in and the past events that have occurred in Nauru.

Mark Issacs, a former Salvation Army employee

"As shocked as we are, we feel it was an incident that was inevitable considering the conditions that the men are kept in and the past events that have occurred in Nauru," he said.

He says tension continued to build even after detainees moved out of tents and into accommodation.

"In the past 10 months there have been a number of incidences, two uprisings that I was present for... there's been a building frustration ever since we first arrived," he said.

He believes detainees are being demonised in the aftermath of the riot.

"This is why we spoke out. We fear that the 150 men who are now detained in a Nauruan prison, that a large majority of them may not have acted in any criminal form and we fear that these men will not be given proper access to legal representation," he said.

Riot gear did not arrive in time

It has also been revealed the detention centre's security providers Transfield sought access to riot equipment in October last year, but it was not in use on the night of the riot.

7.30 has correspondence from this company requesting approval back in October last year for permission from the Immigration Department to purchase 40 sets of riot gear including shields, batons and helmets.

The email is dated October 12 and is from Transfield's general manager of property operations, Derek Osborn.

"Following the incident at the site 10 days ago I discussed with Tracy the need for Transfield Services to have available some personal protective equipment for the security staff," the email said.

"We have put some thought to sourcing equipment that is flexible and not as confronting as the more traditional riot equipment. In particular the use of a 'soft' shield that minimises any harm to either the user or the client is a good step forward."

The email appears to also suggests supplying equipment to the Nauru police.

"As I understand the Nauru Police do not have access to this equipment, and as such it could be prudent to add some additional stock to allow them to use and train with the equipment," it said.

7.30 understands the Immigration Department approved the request in December. The equipment was ordered but did not make it to the island in time for last Friday's riot.

Mr Lake says staff had believed the equipment was required.

"Absolutely there were people particularly in the security services who felt that equipment like that was required to maintain good order at a processing centre on Nauru," he said.

Transfield says its focus has shifted since last October and it no longer needs the equipment it ordered.

"Transfield Services focused on its role of managing an orderly evacuation of site personnel," it said in a statement.

"The proof of the soundness of this strategy was that there were only minor injuries to the people involved in last week's incident."

However law enforcement officials say the equipment is needed to manage events like last Friday.